Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, endurance, non-volatility and low power consumption during operation. One type of MRAM is a spin transfer torque random access memory (STT-RAM). STT-RAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction.
FIG. 1 depicts a conventional magnetic tunneling junction (MTJ) 10 as it may be used in a conventional STT-RAM. The conventional MTJ 10 typically resides on a bottom contact 11, uses conventional seed layer(s) 12 and is under a top contact 16. The conventional MTJ 10 includes a conventional antiferromagnetic (AFM) layer 20, a conventional pinned layer 30, a conventional tunneling barrier layer 40, and a conventional free layer 50. Also shown is a conventional capping layer 14. The conventional free layer 50 has a changeable magnetic moment 52, while the magnetic moment 43 of the conventional pinned layer 30 is stable. More specifically, the magnetic moment 32 of the conventional pinned layer 30 is fixed by an interaction with the conventional AFM layer 20.
Conventional contacts 12 and 16 are used in driving the current in a current-perpendicular-to-plane (CPP) direction, or along the z-axis as shown in FIG. 1. Current passing through the conventional pinned layer 30 becomes spin polarized and carries angular momentum. This angular momentum may be transferred to the conventional free layer 50. If a sufficient amount of angular momentum is so transferred, the magnetic moment 52 of the free layer 50 may be switched to be parallel or antiparallel to the magnetic moment 32 of the pinned layer 30.
To improve the performance of STT-RAM, various factors of the conventional magnetic junction 10 are desired to be optimized. For example, the conventional magnetic junction 10 may be engineered for a desired critical current, Ic, for switching a thermally stable conventional free layer 50. The critical current may be estimated by:
      I    c    =            α      η        ⁢                            〈          H          〉                eff                    H        K              ⁢    1.5    ⁢                  ⁢    mA  where <H>eff is the averaged effective magnetic field seen by the precessing magnetic moments of the conventional free layer 50, Hk is the magnetic field necessary to switch the magnetic moment 52 when applied along the easy axis, α is the damping parameter, η is the spin-torque efficiency, and 1.5 mA represents current and is appropriate to a thermal stability factor (ΔE/kBT) of 60, where ΔE represents the energy barrier for thermal switching, kB is Boltzmann's constant and T is the absolute temperature.
The conventional magnetic junction 10 may be optimized to improve the critical current. Engineering the conventional magnetic junction 10 may include use of CoFe and/or CoFeB for the conventional pinned layer 30 and the conventional free layer 50. CoFe and CoFeB tend to have in-plane magnetic moments, as shown by the magnetic moments 32 and 52. In addition, the conventional tunneling barrier 40 is typically crystalline MgO. The combination of CoFe and CoFeB with MgO may result in a lower critical current.
Although the conventional magnetic tunneling junction 10 functions, further improvements are desired. For example, magnetic junctions usable in magnetic memories that may be smaller, scalable to smaller dimensions, use a lower critical current, may be simple to fabricate, and/or have other properties are desired.
Accordingly, what is desired is an improved magnetic junction usable in higher density STT-RAM.